According to the blog, ”The mantra we keep coming back to when designing Battlefield 3 is “play it your way”. What that means is there’s an unprecedented flexibility in how you tailor your kits. The playable classes are not rigidly defined in what they are supposed to play like. While all four classes in Battlefield 3 (Assault, Engineer, Support, Recon) start out with everything they need to be an efficient soldier in the field, it is totally up to you and your personal preferences how you want to tailor them.
Take the Assault class, for example. As you may know by now, this is now the class that has the ability to equip both a defibrillator and medkit for frontline medic abilities. But if you would prefer to switch your add-ons to, say, an underslung grenade launcher with 40mm grenades, go ahead! That will give you an Assault soldier with a more offensive set of capabilities than the player who opts for the default medic approach.”
Check out the full blog entry here.